What is Huygens' principle?

What is Huygen's principle?

What is Huygen's principle? Show that at a larage distace from the source, a small portion of the spherical wave can be approximated by a plane wave.

What is the importance of Huygens' principle?

State Huygens' Principle.

What are the two assumptions on which Huygens' principle is based? Explain Huygen's geometrical construction for the wavefronts.